Preparation And Properties Of NBR/PA12 Thermoplastic Vulcanizates

A series of butadiene-acylonitrile (NBR)/nylonl2 thermoplastic vulcanizates were prepared by dynamic vulcanization. The experimental results showed that the thermoplastic vulcanizates exhibited excellent comprehensive mechanical properties, the good oil resistance and repetitive processing property, repectively.1. The formulation of NBR/PA12 TPV was studied by two-mill(1) The effects of different curing systems including SP1045/SnCl2, DTDM/CZ and HVA-2/DM were dicussed. The results showed that HVA-2/DM system has a lower curing speed than SP1045/SnCl2 and DTDM/CZ. A curing time of 15 min was necessary. HVA-2/DM TPV has a unique microscopic structure. NBR particles were dispersed in continuous phase PA12 and the size of the particles was less than 1μm. The DSC and rheology result demonastrated that HVA-2/DM TPV had the highest relative crystallinity of PA 12 and the best rheological property. Additionally, TPV cured by SP1045/SnCl2 and DTDM/CZ system has a cocontinuous phase, and a curing time of 10 min was desirable. (2) We also studied the effect of different mass ratios of NBR/PA12. The results revealed that the hardness, tensile strength, tear strength, compression set and oil resistance increase as the mass ratio of NBR/PA12 increase. The size of NBR particles decrease as the mass ratio of NBR/PA12 increase. A mass ratio of 70/30～60/40 was optimum.(3) The effects of NBR variety were investigated. The results declared that the value of polarity of NBR was higher by increasing the loadings of acrylonitrile. The increasing polarity made NBR has a good compatibility with PA 12, which improved the properties of TPV. NBR (41%AN) was optimum.(4) In order to reduce hardness, increase elasticity, and make rheological properties much better, the effects of DOP, LNBR and PPA plasticizers were investigated. The results indicated that the plasticizers functioned as expected, and had little impact on oil resistance. LNBR and PPA plasticizers could not be easily extracted by organic solvent. A formulation of 5～10phr was optimum.(5) The problem of Sticking-to-mill roll of NBR/PA12 TPV existed in the blending process of NBR and PA12. Therefore, mould release agent, oxidized polyethylene wax (316A), was added to the blendings. The results demonstrated that 316A leaded a positive role. The elongation at break was improved dramatically. What is more, a formulation of 5phr was optimum.2. The effects of blending processing technology of two-mill, Haake rheometer and twin screw extruder on the mechanical property and microstructure of TPV were studied at the mass ratio of 70/30,65/35 and 60/40 NBR/PA12. The results showed that the hardness, tensile strength and oil resistance of TPV prepared by two-mill and Haake rheometer were enhanced more apparently compared with those of twin screw extruder. The NBR particles size of TPV by two-mill is the smallest among three preparation methods and NBR particles were dispersed homogeneously within PA 12. The NBR particles of TPV prepared by twin screw extruder also have a good dispersion and the size was much larger.3. The effects of rotation rate and temperature of twin screw extruder were invetigsted. The results indicated that tensile strength and elongation at break were optimum at 300rpm. The time that the blends in twin screw extruder decreased when the rotation rate was more than 400rpm, which result in NBR curing incompletely. A rotation rate of 200-400rpm was optimum. Although high temperature was good for curing and dispersing in PA12, it induced the thermal degradation of blends.4. Furthermore, the repetitive processing property of TPV was discussed. The results revealed that the TPV has excellent repetitive processing property. After repetitive processing for four times, the TPV still exhibited good mechanical property and oil resistance property.